X-ray spectrographic apparatus having a pair of X-ray tubes with different emission properties



April 26. 1966 PlTCHFORD 3,248,543

XRAY SPECTROGRAPHIC APPARATUS HAVING A PAIR OF X-RAY TUBES WITH DIFFERENT EMISSION PROPERTIES 2 Sheets-Sheet 1 Filed April 18, 1963 INVENTOR.

4/?77/01? M P/TCl/FO/PD BY7M;7

April 26, 1966 PITCHFQRD 3,248,543

X-RAY SPECTROGRAPHIC APPARATUS HAVING A PAIR OF X-RAY TUBES WITH DIFFERENT EMISSION PROPERTIES 2 Sheets-Sheet 2 Filed April 18, 1965 7 INVENTOR.

United States Patent 3,248,543 X-RAY SPECTROGRAPHIC APPARATUS HAVING A PAER 0i X-RAY TUBES WITH DIFFERENT EMISSEON PROPERTIES Arthur H. Pitchford, 5881 Lorene Drive, Bethel Park, Pa. Filed Apr. 18, 1963, Ser. No. 273,871 3 Claims. (Cl. 250-515) This invention relates to X-ray spectrographic apparatus and more particularly to X-ray spectrographic apparatus having a plurality of X-ray emitting means for producing X-radiation of different wave lengths and wherein each of the X-ray emitting means may be positioned in radiating relation with the specimen to be analyzed.

In X-ray spectrography, an X-ray tube is employed which radiates a specimen with a primary beam of X- radiation. The primary beam of X-radiation causes the various elements present in the specimen to emit their characteristic X-ray spectra as secondary radiation. The secondary radiation is directed onto an analyzing crystal which separates the various wave lengths of the secondary radiation. The analyzing crystal may comprise, as for example, a single crystal of lithium fluoride, sodium chloride, EDDT or topaz. The sets of atomic planes of the crystal lattice are spaced at a suitable distance so that the analyzing crystal serves as a diffraction grating which will separate the various wave 'lengthscomprising the secondary radiation emitted by the specimen.

As is well known, each element has its own characteristic X-ray spectrum. The wave lengths vary in a regular order from one element to another, i.e., the wave lengths decrease as the atomic numbers increase. Hence, each element present in a specimen may be identified by detecting radiation of each Wave length at its corresponding angular position. The long wave lengths are dispersed to high angles while the shorter wave lengths are dispersed to lower angles,

A proportional or flow proportional counter, or a scintillation counter may be employed to detect the X- radiation reflected by the analyzing crystal at different angles. Hence, the analyzing crystal and the counter must be rotated to scan the desired angular .region for each element. By recording the number of counts produced in the detector, a quantitative analysis may be made of the elements present in the specimen.

As stated above, the wave lengths vary in regular order from one element to another, i.e., the wave lengths decrease as the atomic number of the elements increase. The wave lengths are classified as soft X-rays which include the longer wave lengths and hard X-ray which include the shorter wave lengths. The secondary radiation emitted by each of the elements having atomic numbers from 11 to about 22 is relatively long and therefore is classified as soft radiation. The secondary radiation emitted by each of the elements having atomic numbers from about 22 and higher is relatively short and therefore is classified as hard radiation. Hence, most X-ray spectrographic apparatus employ two crystals mounted in such a manner that each may be moved into the path of the secondary radiation emitted by the specimen. As for example, an EDD-T crystal, having relatively wide spaced atomic planes, may be employed in the diffraction of soft radiation and a lithium chloride crystal, having relatively closely spaced atomic planes, may be employed in the diffraction of hard radiation.

In order to maximize the intensity of the secondary radiation emitted by the elements in the specimen, it has been a common practice to employ one X-ray tube which emits hard radiation for the detection of the higher atomic number elements and another X-ray tube which emits soft radiation for the detection of the lower atomic number elements. As for example, an X-ray tube having a tungsten target will emit hard radiation and an X-ray tube having a chromium target will emit soft radiation.

Present day X-ray spectrographic apparatus uses only one X-ray tube at a time which is rigidly mounted and prealigned in radiating relation with the specimen. This X-ray tube normally employs a target formed from tungsten, platinum, molybdenum or the like, which emits hard radiation. Should the technician desire to employ an X-ray tube which emits soft radiation, he must remove the mounted X-ray tube and install another X-ray tube having a target formed from chromium, aluminum or the like. The removal and installation of X-ray tubes is a time consuming operation which requires disconnecting coolant conduits and the power cable as well as disconnecting the X-ray tube from its support. To install an X-ray tube, the coolant conduits must be reconnected and checked for leaks, the power connection must be made as well as physically securing the X-ray tube to its support. In vacuum systems all seals must be checked for leaks. Furthermore, since an X-ray tube is an expensive piece of equipment, the fewer number of times it is handled the lesser are the chances of damaging it.

Modern steel mills, for example, employ X-ray spectrographic apparatus for analyzing samples of the steel which are taken during its manufacture. Each heat of steel, then, must be held up until each sample is analyzed. It will be appreciated, then, that the time consuming operation of exchanging one X-ray tube for another is an undesirable feature of present day X-ray spectrographic apparatus.

Still another disadvantage of X-ray spectrography concerns the reflection of the X-radiation emit-ted by the X-ray tube. As hereinbefore stated, each specimen will emit secondary radiation which is characteristic of the elements present therein when the sample is radiated with a primary beam of X-radiation. However, a portion of the primary beam of X-radiation also will be reflected by the specimen. Hence, the record produced by the detector on a strip chart, as for example, will include an indication of the presence of a major quantity of the element from which the X-ray tubes target is made. This indication is usually ignored by the technician in his analysis of the specimen. It should be appreciated, then, that if the specimen contains a quantity of the same element from which the X-ray tubes target is made, the secondary radiation emitted by this element will be added to the reflected radiation of the primary beam and hence will be lost. This should be evident since the technican has no way of knowing just how much of the indicated quanti-ty'of the element corresponds to the quantity of the element present in the specimen. The X-ray spectro-graphic apparatus provided by this invention overcomes this disadvantage. I

Accordingly, the primary objects of the present invention includei To provide an X-ray spectrograph which is capable of detecting the lower atomic numbered elements as well as the higher atomic numbered elements;

To provide an X-ray spectrograph having a plurality of X-ray tubes each of which is capable of emitting a different type of X-radiation for the most optimum detection of the lower and higher atomic numbered elements;

To provide an X-ray spectrograph which is capable of detecting the elements from which the X-ray tubes targets are made; and

To-provide an X-ray spectrograph having a plurality of X-ray tubes each of which may be quickly and easily positioned in radiating relation with the specimen being analyzed.

These and other objects and advantages of the present invention will become apparent from the following detailed description by reference to the accompanying drawings, in which:

FIGURE 1 is a fragmentary elevation view, partly in cross section, of the present X-ray spectrograph;

FIG. 2 is an end elevation view of the apparatus of FIG. 1;

FIG. 3 is a fragmentary cross-sectional view, taken along the line 33 of FIG. 1;

FIG. 4 is a fragmentary cross-sectional view illustrating an indexing means employed in the present X-ray spectrograph;

FIG. 5 is an elevation view schematically illustrating the coolant connection of the X-ray tubes of FIG. 1;

FIG. 6 is a cross-sectional view, taken along the line 66 of FIG. 7, illustrating an alternative configuration of the present X-ray spectrograph;

FIG. 7 is a cross-sectional view, taken along the line 77 of FIG. 6, further illustrating the alternative configuration of FIG. 6;

FIG. 8 is a bottom view illustrating a further alternative configuration of the present X-ray spectrograph; and

FIG. 9 is a cross-sectional view, taken along the line 9-9 of FIG. 8, further illustrating the alternative configuration of FIG. 8.

Referring now to FIGS. 1 and 2, an X-ray spectrograph, generally indicated by the numeral 10, comprises a main housing 12 having an open-ended chamber 14 and a cover 16 having a sample entrance port (not visible) which is covered by means of a cap member 18. Within the cover 16 there is a turret-type specimen carriage 20 on which a plurality of specimen holders 22 (only one shown) are supported. The specimen holder 22 carries a'specimen 24 at the open end 26 thereof. A handle 28 is connected to the specimen carriage 20 and serves to successively rotate each specimen 24 into the position shown in FIG. 1.

The X-ray spectrograph is provided with a pair of X-ray tubes 30, 32 having head portions 34, 36 which reside within the chamber 14 and which are secured together in abutting relation by any suitable means. of the head portions 34, 36 includes a window 38 through which a primary beam of X-radiation is directed onto the specimen 24. In the X-ray spectrograph 10, the X-ray tube 30 emits hard radiation and has a target which preferably is formed from tungsten. Alternatively, the target of the X-ray tube 30 could be formed from platinum or molybdenum. The X-ray tube 32, on the other hand, emits soft radiation and has a target which preferably is formed from chromium. Alternatively, the target of the X-ray tube 32 could be formed from aluminum or copper or other lower atomic numbered elements. Hence, the X-ray spectrograph 10 is capable of detecting not only the higher atomic numbered elements through the use of the X-ray tube 30 but also is capable of detecting the lower atomic numbered elements through the use of the X-ray tube 32. The X-ray spectrograph 10 is capable of detecting the lower atomic numbered elements with higher sensitivity particularly when these lower atomic numbered elements are present in trace quantities. It should be evident then that the present X-ray spectrograph has a greater versatility than any prior art X-ray spectrograph.

As illustrated in FIG. 1, the X-ray tube 30 has its head portion 34 disposed in radiating relation with the specimen 24. As can be seen, the X-ray tube 30 extends outwardly through an opening 40 in one wall of the Each 4 housing 12 and is slideably supported on a tube mount assembly 42. Similarly, the X-ray tube 32 extends outwardly through an opening (not visible) in the housing 12 and is slideably supported on a similar tube mount assembly 42.

A bellows seal 44 is provided for each X-ray tube 30, 32 which has one of its ends secured to the body of the X-ray tube in sealed relation therewith by means of a strap clamp 46. The other end of the bellows seal 44 is clamped between a ring member 48 and the wall of the housing 12 by means of a plurality of fasteners 59 which extend through the ring member 48 and the end of the bellows seal 44 and which are threaded into the wall of the housing 12. The bellows seal 44 preferably is formed from resilient material such as rubber and the like. The need of a seal such as the bellows seal 44 will become apparent later in the specification.

Reference is now directed to FIGS. 1, 2 and 3, wherein the preferred construction of the tube mount assemblies 42 is illustrated. Each tube mount assembly 42 generally comprises a tube aligning member 52, a cover strap 54, and a cradle member 56.

The tube aligning member 52 comprises a pair of semicircular members 58 each having a flange 60 extending from each side thereof. The semicircular members 58 are placed around the X-ray tube in opposed relation and a plurality of fasteners 62 (one shown in FIG. 3) are employed to rigidly clamp the semicircular members 58 to the X-ray tube.

The cradle member 56 comprises an arcuate portion 64 whose upper ends are provided with shoulders 66 which are adapted to receive and support the flanges 60 of the tube aligning member 52 in sliding engagement therewith. The cradle member 56 also includes a support arm 68 which is secured to the housing 12 by means of bolts 70.

The cover strap 54 is semicircular in shape and is pivotally secured at one flanged end 72 to the cradle member 58 by hinge means 74 and is secured at the other flanged end 76 to the cradle member 58 by means of a thumbscrew 78. The cover strap 54 is shown in a raised position in phantom outline in FIG. 2.

The cover strap 54 cooperates with the arcuate portion 64 of the cradle member 56 to permit the X-ray tube to move only in a longitudinal direction, i.e., toward or away from the chamber 14 of the housing 12. The shoulders 66 and the flanged ends 72, 76 of the cover strap 54 serve as guideways for the flanges 60 of the tube aligning members 52 and also prevent rotation of the X-ray tubes 30, 32 about their longitudinal axes.

Referring now to FIGS. 1 and 4, the tube mount assembly 42 associated with the X-ray tube 30 also is provided with an indexing means 80 which limits the amount of longitudinal movement through which the Xray tube 30 may move whereby the window 38 thereof is aligned in radiating relation with the specimen 24. The indexing means 80 comprises a ball 82 which is biased toward the tube aligning member 52 by means of a spring member 84. The lower semicircular member 58 of the tube aligning member52 is provided with a pair of detents 86a, 86b into which the ball 82 may enter. The detents 86a, 86b are spaced apart by a predetermined distance which is equal to the distance between the centerlines of the windows 38 of the X-ray tubes 30, 32. The purpose of these detents will become apparent later in the specification. In any event, when the X-ray tube 30 is moved, a click will be heard each time the ball 82 engages one of the detents 86a, 86b.

Referring now to FIGS. 1 and 5, each of the X-ray tubes 30, 32 requires a coolant to be circulated internally thereof in order to cool the target. As can be seen in FIG. 5, each of the X-ray tubes 30, 32 has a coolant inlet port 88 and a coolant outlet port 90. As schematically illustrated, rigid conduits 92 leading from the inlet ports 88 are connected to a flexible conduit 94 which extends from a supply port 96 in the housing 12. Similarly,

rigid conduits 98 are Connected to a second flexible conduit 100 which extends from a discharge port 102 in the housing 12. Since the conduits 92 and 98 are rigid, they serve the secondary function of coupling the X-ray tubes 30 and 32 together in arigid manner. Since the conduits 94 and 100 are flexible, the X-ray tubes 30 and 32 are'free for longitudinal movement.

In operation, then, the technician places a number of the samples 24 in the specimen holders 22. To analyze each of the specimens 24 for elements having atomic numbers from about 22 and higher, the technician employs the X-ray tube 30 in the position illustrated in FIG. 1. When this analysis is completed, the technician need only slide the X-ray tubes 30, 32 to the left until a click is heard (ball 82 engages detent 86b) which indicates that the window 38 of the X-ray tube 32 is in radiating relation with the specimen 24 being analyzed. The technician proceeds with his analysis of the elements having atomic numbers from 11 to about 22. It should be noted that the bellows seals 44 permit the X-ray tubes 30, 32 to be moved without breaking the seal provided thereby. Hence, the X-ray spectrograph may be employed to analyze specimens either at atmospheric pressure or under a vacuum.

Alternatively, the X-ray tubes 30, 32 may be mounted on the X-ray spectrograph 10 on a rotatable carriage means whereby they may be rotated into radiating relation with the specimen 24. This alternative arrangement is illustrated in FIGS. 6 and 7. Corresponding numerals will be employed to identify corresponding parts already described.

Referring to FIGS. 6 and 7, an X-ray spectrograph 10' has a rotatable carriage means 104 which is employed to support the X-ray tubes 30, 32 in spaced, side-by-side, substantially parallel relation. The rotatable carriage means 104 comprises a rotatable plate 106 having a peripheral flange 108 engaged with a wall 110 of the main housing 12. The rotatable plate 106 is positioned within an opening 112 of the wall 110 and is rotatable therein. An annular plate 114 is secured to the wall 110 preferably by means of bolts 116 and includes an inwardly extending flange 118 which engages the peripheral flange 108 of the rotatable plate 106 with a slight pressure whereby the plate 106 may be rotated. An O-ring seal 120 is provided between the peripheral flange 108 and the wall 110.

As can be seen the X-ray tubes 30,-32 extend through and are supported by annular hub members 122. A seal plate 124 is secured to the rotatable plate 106 by means of bolts 126 and includes annular hub member 128 through which the X-ray tubes 30, 32 extend. O-ring seals 130, 132 are provided for sealing the seal plate 124 against the entry of air. The O-ring seals 120, 130, 132 are especially important when the chamber 14 of housing 12 has been evacuated.

The rotatable carriage means 104 maintains the head portion 34 of the X-ray tube 30 in radiating relation with the specimen 24 disposed in the specimenholder 22. When it is desired to employ the X-ray tube 32, the technician merely rotates the X-ray tube 32 into radiating relation with the specimen 24. Although not illustrated in FIGS. 6 and 7, an indexing means similar to the indexing means 80 hereinbefore described preferably is provided as a means for indicating the proper alignment of each of the X-ray tubes 30 or 32 with respect to the sample 24.

In FIG. 7, a collimator 132 is secured to the housing 12 and is aligned with the specimen 24 to direct the secondary radiation onto an analyzing crystal (not shown).

The X-ray spectrograph 10' has been illustrated supporting two X-ray tubes. Alternatively, more than two X-ray tubes may be supported by the rotatable carriage means 104. As can be seen in FIG. 7, two other X-ray tubes 30' and 32' are shown in phantom outline in the position in which they would be supported by the rotatable carriage means 104.

FIGS. 8 and 9 illustrate a further alternative configuration of the present invention. An X-ray spectrograph 10" includes the housing 12 provided with the rotatable carriage means 104 hereinabove described. The rotatable carriage means 104 supports X-ray tubes 134, 136, 138 and 140 in vertical substantially parallel side-by-side relation. Each of the X-ray tubes 134, 136, 138 and 140 includes a head portion 142 having an end window 144 through which X-radiation is emitted in a direction which is parallel to the longitudinal axis of the X-ray tube. In this instance, the specimen holder 22 supports the specimen 24 directly above the end window 144 of the X-ray tube 138. The collimator 132 is aligned with the specimen 24 and directs the secondary radiation onto an analyzing crystal (not shown).

In this configuration, the X-ray tubes 134 and 136 may comprise hard emitters while the X-ray tubes 138 and 140 comprise soft emitters. That is to say, the targets of the X-ray tubes 134 and 136 may be formed from tungstenand platinum respectively which are hard emitters while the targets of the X-ray tubes 138 and 140 may be formed from chromium and copper respectively, Hence, the technician may employ the X-ray tube 134 (tungsten target) for the detection of the higher atomic numbered elements present in the specimen 24 with the exception of tungsten. The technician may then rotate the X-ray tube 136 (platinum target) into radiating relation with the specimen 24 for the detection of the element tungsten. Similarly, the technician may employ the X-ray tube 138 (chromium target) by merely rotating it into radiating relation with the specimen 24. The X-ray tube 138 may be used to detect the lower atomic numbered elements present in the specimen 24 with the exception of chromium. To complete his analysis of the specimen 24, the

technician may then rotate the X-ray tube 140 (copper.

target) into radiating relation with the sample 24 for the detection of the element chromium.

Although not shown in FIGS. 8 and 9, an indexing means similar to the indexing means hereinabove described preferably is provided as a means for indicating the proper alignment of each of the X-ray tubes 134, 136, 138 and with respect to the sample 24.

Although the invention hasbeen shown in connection with certain specific embodiments, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

I claim as my invention:

1. In X-ray spectrographic apparatus, the combination comprising a pair of separate generally tubular X-ray tubes, one of said X-ray tubes having a head portion incorporating vmeans for emitting relatively soft X-radiation and the other of said X-ray tubes having a head portion incorporating means for emitting relatively hard X-radiation, and carriage means supporting said pair of tubular X-ray tubes in substantially coaxial head portion-to-head portion abutting relationship for movement along the axes of the tubes, whereby the X-radiation emitting means in a selected one of said tubes may be moved into radiating relation with a specimen to be analyzed.

2. In X-ray spectrographic apparatus, the combination comprising a pair of separate X-ray tubes each having a head portion from which X-radiation is emitted in a direction which is transverse to the longitudinal axis of its associated X-ray tube, one of said X-ray tubes being capable of emitting relatively soft X-rays and the other of said X-ray tube-s being capable of emitting relatively hard X-rays, carriage means for movably supporting said pair of X-ray tubes in axially aligned, head portion-to-head portion, generally abutting relation, and means for rigidly connecting said pair of X-ray tubes whereby a selected one of said pair of X-ray tubes may be moved on the carriage means into radiating relation with a specimen to be analyzed.

3. In X-ray spectrographic apparatus, the combination comprising a pair of separate X-ray tubes each having a head portion from which X-radiation is emitted in a direction which is transverse to the longitudinal axis of the X-ray tube, one of said X-ray tubes being capable of emitting relatively soft X-rays and the other of said X-ray tubes being capable of emitting relatively hard X-rays, carriage means for movably supporting said pair of X-ray tubes in axially aligned, head portion-to-head portion, generally abutting relation, said carriage means including a main housing which encloses said generally abutting head portions, specimen supporting means in the housing, tube mount assemblies on opposite sides of said housing for supporting the respective ends of said X-ray tubes which are opposite said generally abutting head portions, and means for rigidly connecting said pair of X-ray tubes whereby either one of said pair of X-ray tubes may be moved on said tube mount assemblies into a position where the X-radiation emitted from its head portion is directed onto a specimen supported on said specimen supporting means.

References Cited by the Examiner UNITED STATES PATENTS 2,884,535 4/1959 Swift 250--83.6 2,884,538 4/1959 Swift 250-52 X 2,884,539 4/1959 Swift 250106 X 2,948,822 8/1960 Paroselli 31356 3,114,832 12/1963 Alvarez 250-515 FOREIGN PATENTS 858,416 1/1961 Great Britain. 858,417 1/1961 Great Britain.

63,432 12/ 1912 Switzerland.

RALPH G. NILSON, Primary Examiner.

20 ARCHIE R. BORCHELT, Examiner. 

1. IN X-RAY SPECTROGRAPHIC APPARATUS, THE COMBINATION COMPRISING A PAIR OF SEPARATE GENERALLY TUBULAR X-RAY TUBES, ONE OF SAID X-RAY TUBES HAVING A HEAD PORTION INCORPORATING MEANS FOR EMITTING RELATIVELY SOFT X-RADIATION AND THE OTHER OF SAID X-RAY TUBES HAVING A HEAD PORTION INCORPORATING MEANS FOR EMITTING RELATIVELY HARD X-RADITION, AND CARRIAGE MEANS SUPPORTING SAID PAIR OF TUBULAR X-RAY TUBES IN SUBSTANTIALLY COAXIAL HEAD PORTION-TO-HEAD PORTION ABUTTING RELATIONSHIP FOR MOVEMENT ALONG THE AXES OF THE TUBES, WHEREBY THE X-RADIATION EMITTING MEANS IN A SELECTED ONE OF SAID TUBES MAY BE MOVED INTO RADIATING RELATION WITH A SPECIMEN TO BE ANALYZED. 